This invention relates to communication systems and, more particularly, to communications systems for transmitting message-waiting and/or do-not-disturb signals between one or more remote communication stations and a central communication station. One application of this invention illustrated and described herein is a telephone related communication system for providing two-way communication between a group of remote telephone stations and a central telephone receptionist or operator station -- do-not-disturb and/or message-received signals (the inverse of message-waiting signals) passing individually from the remote station to the central station, and message-waiting signals passing individually from the central station to the remote stations. The invention, however, may be utilized in other applications and environments.
The concepts of message-waiting or do-not-disturb, or combination message-waiting and do-not-disturb communication, heretofore have been applied principally to private branch exchange (PBX) telephone systems. In the PBX systems disclosed in U.S. Pat. Nos. 3,564,148 and 3,826,876, the central switchboard operator controls both the message-waiting and do-not-disturb indications, the latter in response to a request from a subscriber, using couplex switching and access circuitry. Generally similar message-waiting indications are provided for PBX application in the systems disclosed in U.S. Pat. Nos. 3,934,098, 3,532,832, 3,050,592 and 2,884,491.
A message-waiting lamp control circuit for so-called "key telephone" application is disclosed in U.S. Pat. No. 3,743,792. (Key telephone equipment is characterized by line pick-up, hold keys and signalling lamps mounted by the base of the telephone set and generally is utilized to provide intercom service among two or more subscriber telephone stations -- the switching functions being initiated manually by actuation of the appropriate pick-up or hold key.) Compared to the PBX related systems mentioned hereinabove, this circuit offers simplified control functions; however, it offers only limited versatility from the standpoints of the type of information which can be transmitted and the manner in which it is transmitted. The circuit essentially affords only message-waiting or message-received (the inverse of message-waiting) communication between two key telephone stations using a signalling path made up of two electrical leads, plus ground, and one lamp at each station. It utilizes key telephone operations in the form of momentary key depressions to control message-waiting lamp indications at the called and calling sets. Additional telephone-related communications systems are disclosed in U.S. Pat Nos. 3,819,873, 3,784,721, 3,683,121, and 3,320,368.